1. Field of the Invention
The present invention relates to a process for producing a copolyester from a lower dialkyl ester of a terephthalic acid (LDE), a glycol (GLY) and a dicarboxylic acid (DA). Using a specific catalyst system of the present invention allows to conveniently produce the copolyester by sequencing an ester interchange and direct esterification. In particular, the catalyst system comprises manganese (Mn), lithium (Li), antimony (Sb) and optionally cobalt (Co). More specifically, manganese and lithium are used as catalysts for the ester interchange of the LDE and GLY, lithium for the direct esterification of DA and GLY, while lithium cobalt and antimony are used as catalysts for the polycondensation stage. The manganese is sequestered after the ester interchange. It has been found a copolyester can be produced by adding a slurry of DA/GLY to the reaction product of LDE and glycol of the ester interchange, reacting the DA/GLY slurry by direct esterification therein and copolymerizing the two reaction products.
Furthermore, copolyesters of the present invention are demonstrated to have improved melt flow characteristics and in solid form, improved cutting characteristics during processing and increased tensile strength when bonded in a blend with other polyester fibers.
Copolyesters of the present invention can be used as binder fibers in nonwoven applications or can be used in conjunction with polyester fiber in bicomponent fibers.